<!DOCTYPE html>
<html lang="en">

<head>
  <meta charset="UTF-8">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>Document</title>
</head>

<body>
  <div id="test"></div>

  <script src="./js/react.development.js"></script>
  <script src="./js/react-dom.development.js"></script>
  <script src="./js/babel.min.js"></script>
  <script type="text/babel">
    function Demo() {
      let num = 10

      const sum = () => {
        num++
        console.log(num)
      }

      const del = () => {
        num--
        console.log(num)
      }

      return (
        <div>
          <div
            style={{ color: 'green', backgroundColor: 'red' }}>{num}</div>
          <button onClick={sum}>+1</button>
          <button onClick={del}>-1</button>
        </div>
      )
    }

    ReactDOM.render(<Demo />, document.getElementById('test'))
  </script>

</body>

</html>